Proppants are used to keep open fractures created by hydraulic fracturing of a subterranean formation, e.g., in an oil or gas bearing strata. Typically, the fracturing is performed in a subterranean formation to increase oil or gas production. Fracturing can be caused by injecting a viscous fracturing fluid (frac fluid) at a high pressure into the well. As fractures are formed, a particulate material, referred to as a “propping agent” or “proppant” is placed in the formation to maintain the fracture in a “propped” open condition when the injection pressure is released. As a fracture forms, the proppants are carried into the well by suspending them in a fluid and filling the fracture with the slurry of proppant particles. Upon release of the pressure, the proppants lodge in the fractures so that the fractures do not close once fracturing pressure is reduced. Using proppants increases production of oil and/or gas from a subterranean formation by providing highly conductive channels through the formation for the oil and/or gas to flow to the well head.
The maintenance of these channels provides increased flow of various fluids, e.g., hydrocarbons such as natural gas and oil.
Proppant materials that have been widely used include: (1) particulate sintered ceramics, typically aluminum oxide, silica, or bauxite, often with clay-like binders or other additives to increase the particulate's compressive strength, especially sintered bauxite; (2) natural, relatively coarse, sand, the particles of which are roughly spherical, generally called “frac sand” and (3) resin-coated particulates of (1) and (2), i.e., resin-coated proppant.
One of the problems commonly encountered when using these and other such proppant materials for maintaining the fractures created in a subterranean formation in an open condition is the flow back of both proppant and other particulates through the formation with the hydrocarbon being recovered.
One approach for inhibiting such flow back centers on the use of a coated proppant, where the proppant is coated with a thermosetting resin composition. The resin is intended to cure in place creating a hard permeable mass when the proppant is lodged in the formation. Typically, the resin-coated proppant is deposited in the fractures after a large quantity of uncoated proppant material has first been deposited. In other words, the last portion of the proppant deposited in each fracture, often referred to in the art as the “tail-in” portion, constitutes the proppant coated with the thermosetting resin. Upon curing the resin, the tail-in portion of the proppant is consolidated into a hard permeable mass having a high compressive strength. With that structure in place, unconsolidated proppant and formation particulate solids are hopefully prevented from flowing out of the fractures with the recovered hydrocarbons.
Another approach to reducing the occurrence of particulate flow back is described in co-pending U.S. Application Ser. No. 11/456,897, published as US 2008-0011477 A1. In accordance with that invention, the proppant is provided with a coating of a thermoplastic resin adhesive. One particularly preferred class of thermoplastic materials is those substances commonly referred to as hot melt adhesives. By using such materials, the coating on the proppant exhibits a latent tackiness, i.e., the tackiness of the coating does not develop until the proppant is placed into the hydrocarbon-bearing formation. The latent tackiness aids in the ease of handling of this coated proppant prior to down well placement where aggregation then occurs as the thermoplastic coating thereafter softens or at least partially fuses to cause the tacky (sticky) material (adhesive) to produce agglomerates as particulates bridge one-to-another thus forming a stable framework within the fracture to provide a fluid permeable region within the subterranean formation.
U.S. Pat. No. 6,116,342 describes still another approach which attempts to provide flow back control in well fracture operations. According to the disclosed method, a combination of a proppant and a separate magnetized material is placed in the formation fractures. The magnetized material is comprised of a magnetizable metal which can be in the form of beads, fibers, strips, particles or the like, or the metal can be embedded in or coated on a non-metallic material. As the magnetized material moves into voids or channels located within the proppant bed through which both deposited proppant and natural formation particulates can flow from the formation, the magnetized material forms clusters which are held together by magnetic attraction. These clusters purportedly facilitate the formation of permeable proppant bridges. Such magnetized material-proppant bridges then impede the flow-back of proppant and formation solids, while allowing hydrocarbon flow through the formation.
This prior patent indicates that the magnetized material utilized with a particular sized proppant should have a similar size to the proppant in order to insure that the proppant bed containing the magnetized material has sufficient permeability. The patent also suggests that the magnetized material be included in a fracture or fractures with the proppant in an amount in the range of from about 0.1% to about 25% by weight of the proppant, and preferably ranges from 1% to 5% by weight of proppant.
While these techniques can be applied in an effort to control the undesired flow of solids through the formation during hydrocarbon recovery operations, the art continues to search for other techniques of fracturing and placing proppant in subterranean formations in a way to limit flow-back of both proppant and formation solids with the recovered hydrocarbon fluid.